Hydration sensors for monitoring and diagnosis of skin diseases in any environment

Patent metadata

Field	Value
Publication number	US-2024023882-A1
Application number	US-202118031389-A
Country	US
Kind code	A1
Filing date	Oct 18, 2021
Priority date	Mar 30, 2018
Publication date	Jan 25, 2024
Grant date	—

Abstract

This invention relates to a soft, battery-free, flexible, non-invasive, reusable hydration sensor adherable to even small-areas and curvilinear surfaces of a body. The hydration sensor measures volumetric water content in skin as a function of depth, and wirelessly transmits data to a portable smart device. The hydration sensor includes a top layer for thermal, chemical and mechanical isolation of the hydration sensor from an environment; a bottom layer operably placed on a target area of interest on the skin; and a flexible printed circuit board (f-PCB) disposed between the top layer and the bottom layer. The f-PCB contains electronics for sensing and wireless communication. The bottom layer operably serves as a direct interface between the f-PCB and the skin and comprises a flexible adhesive for attaching the hydration sensor to the skin.

First claim

1 . A hydration sensor, comprising:
a top layer for thermal, chemical and mechanical isolation of the hydration sensor from an environment; a bottom layer operably placed on a target area of interest on skin; and a flexible printed circuit board (f-PCB) disposed between the top layer and the bottom layer, wherein the f-PCB contains electronics for sensing and wireless communication, and the bottom layer operably serves as a direct interface between the f-PCB and the skin and comprises a flexible adhesive for attaching the hydration sensor to the skin.

2 . The hydration sensor of claim 1 , wherein the electronics comprises:
a heating circuit comprising a heating element for operably heating the target area of interest of the skin; and a sensing circuit comprising a temperature sensor for simultaneously recording a transient temperature change (ΔT) thereof.

3 . The hydration sensor of claim 2 , wherein the heating element comprises a heater comprising at least one resistor.

4 . The hydration sensor of claim 3 , wherein the heater comprises two or more surface-mount (SMT) thin film resistors, thick film resistors, through-hole resistors, and/or ultrathin-film metal resistors connected in series to form a heater.

5 . The hydration sensor of claim 2 , wherein the temperature sensor comprises an SMT negative temperature coefficient thermistor, positive temperature coefficient thermistor, resistance temperature detector (RTD), thermocouple or any other conductive temperature sensor.

6 . The hydration sensor of claim 1 , wherein the heating element and the temperature sensor are arranged from each other by a distance.

7 . The hydration sensor of claim 6 , wherein the distance is determined by the design requirement of depth sensitivity into the skin, and ranges from about 10 μm to about 10 mm.

8 . The hydration sensor of claim 6 , wherein the heater and temperature sensor are the same component, wherein the distance between them is zero.

9 . The hydration sensor of claim 2 , wherein the sensing circuit further comprises a microcontroller (μC).

10 . The hydration sensor of claim 9 , wherein the heater is operably switchable between ON and OFF controlled by the microcontroller.

11 . The hydration sensor of claim 9 , wherein the microcontroller is programmable with custom-designed embedded codes using at least one of near field communication (NFC), Wi-Fi/Internet, Bluetooth, Bluetooth low energy (BLE), and Cellular communication protocols for wireless communication of the hydration sensor to a custom smartphone application.

12 . The hydration sensor of claim 11 , wherein the electronics further comprises a primary antenna tuned to primary frequency, and a secondary antenna.

13 . The hydration sensor of claim 12 , wherein the primary antenna is a transmission coil of an external device that is capable of wireless communications using the NFC protocol.

14 . The hydration sensor of claim 13 , wherein the external device is a smartphone, a tablet, computer or any electronic device with data reading capability.

15 . The hydration sensor of claim 13 , wherein the secondary antenna comprises a first antenna electronically connected to the microcontroller for powering the sensing circuit and for communicating data to the external device using the NFC protocol, and a second antenna electronically connected to the heating circuit for powering the heating element.

16 . The hydration sensor of claim 15 , wherein the first antenna and the second antenna are arranged in a concentric geometry.

17 . The hydration sensor of claim 16 , wherein the first antenna has a quality-factor (Q) that is relatively high to enable good communication distance and coupling across external devices with different primary antennae, and the second antenna has the quality-factor that is relatively low to support adequate power harvesting despite the difference between its resonance frequency and that of the primary coil.

18 . The hydration sensor of claim 17 , wherein the quality-factor of the first antenna is about 11, and the quality-factor of the second antenna is about 8.

19 . The hydration sensor of claim 15 , wherein the first antenna is tuned to the primary frequency, and the second antenna is tuned to a secondary frequency that is different from the primary frequency so as to prevent interference with the first antenna.

20 . The hydration sensor of claim 19 , wherein the primary frequency is a standard NFC frequency of about 13.56 MHz, and the secondary frequency is about 19.04 MHz.

21 . The hydration sensor of claim 1 , being operated using a single antenna.

22 . The hydration sensor of claim 1 , wherein the electronics comprises a generic design including blocks of:
(a) a powering system comprising voltage/power regulators driven by an external battery or magnetic induction to supply power to the heater, sensing and communication circuits; (b) an analog to digital converters (ADC) chip or data modulator to prepare the output of the sensing circuit for transmission to an external readout device; and (c) a transceiver chip having at least one of NFC, Wi-Fi/Internet, Bluetooth, BLE, and Cellular communication protocols to transmit the output signal to the external readout device.

23 . The hydration sensor of claim 1 , having a dynamic temperature range of about 18-45° C., adjustable through an amplifier gain, with a minimum resolution of about 15 mK, limited by the ADC.

24 . The hydration sensor of claim 1 , wherein the f-PCB is formed of a flexible material.

25 . The hydration sensor of claim 24 , wherein the flexible material comprises polyimide (PI), polyethylene terephthalate (PET), or any one of them in combination with a stiff PCB material including FR-4.

26 . The hydration sensor of claim 25 , wherein the f-PCB comprises open spaces and/or mechanical relief cuts for enhancing the overall flexibility, and limiting thermal transport through the PI, away from the sensing components.

27 . The hydration sensor of claim 1 , wherein the bottom layer comprises a flexible adhesive layer bonding to a thin layer of SiO 2 coated on a backside of the f-PCB.

28 . The hydration sensor of claim 1 , wherein the bottom layer adheres to the f-PCB through use of silicone bonding material, epoxy, glue, or commercial adhesive.

29 . The hydration sensor of claim 27 , wherein the bottom layer further comprises an ultrathin fabric of fiberglass or a reinforcement material embedded in the flexible adhesive layer for enhancing mechanical robustness of the hydration sensor.

30 . The hydration sensor of claim 29 , wherein the reinforcement material is flexible and has varying mesh density and thickness to lend tear resistance to the bottom layer.

31 . The hydration sensor of claim 29 , wherein the flexible adhesive layer is formed of silicone or silicone gel, or commercially available double-sided skin-safe adhesives, with the ratio of silicone and silicone gel being adjusted to co-optimize mechanical integrity and tackiness of the adhesive.

32 . The hydration sensor of claim 1 , wherein the top layer is a shell-like top encapsulation layer including small air gaps for thermally, mechanically, and chemically insulating the critical sensing components.

33 . The hydration

Assignees

• Univ Northwestern

Inventors

• Rogers John A
• Banks Anthony R
• Madhvapathy Surabhi Rao
• Wang Heling
• Huang Yonggang
• Xu Shuai

Classifications

• A61B5/443 Primary

  Evaluating skin constituents, e.g. elastin, melanin, water · CPC title

• A61B5/4875

  Hydration status, fluid retention of the body · CPC title

• A61B5/6832

  using adhesives (conductive adhesive for bioelectric electrodes A61B5/259) · CPC title

• A61B5/14521

  using means for promoting sweat production, e.g. heating the skin (measuring sweat secretion A61B5/4266) · CPC title

• A61B5/002

  Monitoring the patient using a local or closed circuit, e.g. in a room or building (A61B5/0017 takes precedence) · CPC title